//#include<stdio.h>
//
//double result_real, result_imag;
//void complex_prod(double x1, double y1, double x2, double y2)
//{
//    result_real = x1 * x2 - y1 * y2;
//    result_imag = x1 * y2 + x2 * y1;
//}
//
//int main()
//{
//    double imag1, imag2, real1, real2;
//    scanf_s("%lf %lf", &real1, &imag1);
//    scanf_s("%lf %lf", &real2, &imag2);
//    complex_prod(real1, imag1, real2, imag2);
//    printf("product of complex is (%f)+(%f)i\n", result_real, result_imag);
//    return 0;
//}